I was part of the Cohort 3 Step Up programme (completed in 2015), and was part of the West London Alliance cohort. I thought I'd respond to a few of the questions as I know I used Student Room when i was applying.
ASSESSMENT DAY: In terms of assessment day that i took part in, it was one-day assessment with four parts: written task, group task, role play and interview. After each task, you were given a sheet to reflect on how you approached the task, what you did well in and how you could improve. Social Work training and practice is very reflective-focused and so you need to demonstrate that you can reflect meaningfully on yourself and your actions.
MAKE-UP OF THE COURSE: there was big variety in people's background, and we did have some on my course who came straight form university (whether BA or MA), but the majority had some level of work experience.
BREAKS ON THE COURSE: When I did the course, we did have weeks here and there to have time off - usually around easter, christmas and before and after placements. I was able to move a couple weeks together and go to Asia for a couple weeks in the summer which was needed as the course is intense.
PLACEMENTS: the course is mainly geared toward Children's Services work, but there were many on my course who went on to work in adults after a couple of years in Childrens Services. We had three placements: a 30 day child-focused placement (mine was in a school), a 70 day adult focused placement (mine was in a community based drug and alcohol center) and a 100 day children's services placement (mine in an assessment team).
I'll try check this thread again if people have any other questions